<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=, initial-scale=1.0">
    <title>Document</title>
    <style>
        .parent{
            width: 500px;
            height: 500px;
            background-color: aqua;
            position: relative;
        }
        .child{
            width: 100px;
            height: 100px;
            background-color: red;
            position:absolute;
            left: 50%;
            top: 50%;
           }
    </style>
</head>
<body>
    <div class="parent ">
        <div class="child"></div>
    </div>
</body>
</html>